Answer: The population of sage-grouse decreases with the passage of time because of humans.
Explanation: In the past, long time ago the population of sage-grouse bird were in millions in the Western United States of America and Canada but gradually decrease occurs in population with the passage of time due to the change which occurs in the environment by humans. Destroying the natural habitat for making buildings and for energy development decrease the population of sage-grouse from 16 million to 500,000 during 100 years.